It offers some 30 to 40% more time (piston dwell near TDC) to the fuel to get prepared and burned efficiently:

Here is a single 4stroke PRE

and here is the Junkers-PRE version

which is absolutely balanced, has 4stroke lubrication, has built-in scavenging pumps, has through scavenging, has more than 2stroke power concentration and top thermal efficiency (the constant volume portion of combustion is significantly increased).

So the idea is that by reducing the length of the con rod, and making it work in tension, you change the graph of piston travel vs crank angle, in a beneficial way.

That's very clever. The disadvantage is that the side force on the piston is higher, but by putting the skirt very remote from the rings you can use a lot better lubrication then is used in a conventional engine.

Originally posted by Greg Locock So the idea is that by reducing the length of the con rod, and making it work in tension, you change the graph of piston travel vs crank angle, in a beneficial way.

That's very clever. The disadvantage is that the side force on the piston is higher, but by putting the skirt very remote from the rings you can use a lot better lubrication then is used in a conventional engine.

Greg,

The connecting rod length, or more correctly the con-rod to piston stroke ratio, can be as much as the conventional engine. For instance with 1.65 con-rod to piston stroke ratio the PRE offers some 35% more time for combustion. The animations have short con-rod (1.1 to 1.3) exactly to show that the shorter the connecting rod, the more time is provided at good conditions for the fuel to get prepared and burned (it is the opposite from what happens in the conventional design, where the longer the connecting rod, the longer the piston dwell at TDC). Take a look at the array at the bottom of the www.pattakon.com/pre/ web page.

In the prototype under construction, the con-rod to piston stroke ratio is selected 1.5 (some old cars used such small con-rod).

The second strong point of the Junkers-PRE (the first is the additional time the piston dwells near TDC) is that it combines two short stroke pistons to form a long stroke cylinder, for instance with 50mm piston stroke the "cylinder stroke" of the Junkers-PRE is 100mm. This means that, for the same con-rod to stroke ratio and at the same rpm, the piston speed and the piston acceleration of the Junkers-PRE with 50mm piston stroke (i.e. 100mm "cylinder stroke") is half than the piston speed and the piston acceleration of the conventional engine with 100mm "cylinder stroke" i.e. 100mm piston stroke.

Originally posted by ray b bottom picture is a bit oddwhere is the fuel injected and or burned ends or middle tooor is the middle the superchargerwhy does the rod poke out of the cylinder

There are three spaces in the Junkers-PRE engine. The middle one is where combustions happens. The other two are the scavenging pumps (look carefully at the one way valves at the left and right enf of the cylinder).

The rode can poke out of the cylinder because at that area nothing else happens and the connecting rod needs some space to move. Where is the problem with this?

Originally posted by Wolf Ray- 'cylinder' is between pistons. Opposed piston (2-stroke diesel) engine was even used in military aircraft (Jumo 205).

Wolf,

the Junkers engine

was used in 2nd world war. Even today conventional direct injection Diesel Junkers are built and used in aviation (search at DAIR). It lacks combustion time exactly as the conventional engine.

But Junkers-PRE is another strory.It provides a lot more time for combustion. It also has buitl-in scavenging pump which changes the behaviour from a constant load / revs engine to an engine capable to operate at a wide range of revs and loads.So, take another look at the PRE.

Good catch Manolis. OK, so the only real negative I can see is that the piston mass will be substantially higher than for a conventional layout. But as I said, the advantage in being able to lubricate the skirt properly may make up for that to some extent.

Originally posted by Wolf Ray- 'cylinder' is between pistons. Opposed piston (2-stroke diesel) engine was even used in military aircraft (Jumo 205).

Opposed-piston engines were also used in ships and submarines, and thousands and thousands of Fairbanks-Morse diesel-electric locomotives. Also an early automobile, the Gobron Brillie. Here is the F-B:

On many of these OP engines like the F-B, the crankshafts were phased 12 to 18 degrees apart, so that one crank took the accessory loads and the other crank provided the power.

Originally posted by McGuire Hey, a pullrod engine. Since I don't see one here, I assume you haven't built a running example as yet. Have you performed any friction and inertia estimates? Any unit weight projections?

In this instant-gratification world everybody seems to want all their questions answered now. For the person who came up with this idea and who is undoubtedly investing himself quite deeply into it, it might make more sense to do a bit of conceptual 'field testing' before getting that far into the nitty gritty number crunching. Which is pretty much what he's doing by posting here, I think.

Originally posted by Greg Locock Good catch Manolis. OK, so the only real negative I can see is that the piston mass will be substantially higher than for a conventional layout. But as I said, the advantage in being able to lubricate the skirt properly may make up for that to some extent.

Good luck with it.

Greg,

About the weight of the double pistons.

Let suppose we separate the double piston of the Junkers-PRE in two independent pistons: one for scavenging and one for combustion. Each one of those two pistons is connected to the existing crankpin by its own connecting rod and its own piston pin (i.e. we have a total of 4 pistons and 4 connecting rods and 4 piston pins to realize this single cylinder “Junkers”) :

Would you ever think that this arrangement has too much reciprocating weight or the inertia loads are too heavy? No. But such an arrangement does not provide the benefits of the Junkers-PRE.

Now think how you get the real Junkers-PRE engine :

(with the two double pistons, the only two connecting rods and the only two piston pins) starting from the “Junkers” above (with the 4 pistons, the 4 piston pins and the 4 connecting rods) : all you have to do is to throw away two connecting rods and two piston pins and to secure the scavenging piston to their mate combustion piston.

Originally posted by McGuire Hey, a pullrod engine. Since I don't see one here, I assume you haven't built a running example as yet. Have you performed any friction and inertia estimates? Any unit weight projections?

A Junkers-PRE direct injection prototype is in progress. Not yet ready.

The reciprocating mass comprises the piston weight, the piston pin weight anf the upper part of the connecting rod (about the 1/3 of con-rod weight).The double piston weight is increased. The connecting rod weight is decreased (its heavy loads from inertia and combustion are in tension only).

For the same "cylinder stroke" with a conventional, the piston of the Junkers-PRE has half the speed and half the acceleration of the conventional piston. Think about it. Also read the previous reply to Greg.

It would probably be difficult to lubricate/cool the pistons with this design. Also, in order to handle the +200 bar peak pressures in a commerical diesel engine, weight of the reciprocating components would most likely also be a problem.

To get a short combustion time, motion of the gas inside the cylinder is important, so some data about this subject would also be needed.

The ideal cycle for the compression ignition engine is a constant pressure or a constant pressure/volume cycle.

The conventional opposed piston engines need long piston stroke and long connecting rods: the lubrication of the piston skirt (which also opens and closes the intake or exhaust ports) is not simple. You need accurate control of the oil that lubricates the piston skirt: less than necessary cannot face the thrust loads, more than necessary escapes through the ports. The long connecting rods decrease the thrust loads and increase slightly the dwell of the piston at TDC. But the long connecting rod is also heavy and increases the total height of the engine. You also need larger and heavier gears (from one end of the engine to the other) to synchronize the two crankshafts.The conventional Junkers engine has another problem: the scavenging process is done with external means (like roots compressors or blowers or …). This adds bulk, friction, cost and, in most cases, gives an efficient breath only in a narrow rev range.

In comparison, the lubrication of the piston skirt of the Junkers-PRE is simple: The cool side of piston and cylinder (where the piston pin is located) can use as much oil as you like. This way shorter and lighter connecting rods can be used (shorter connecting rod provides, in PRE, more dwell of the piston at TDC, i.e. more time to prepare and burn the fuel, i.e. higher efficient rev limit). At the other side, you need oil only for the piston rings.The built-in scavenging pumps offer simplicity, completeness and a wide band range of efficient breathing.A cylinder of 100mm stroke and 80mm bore (or 200mm stroke and 160mm stroke and so on) seems a good choice. It gives compact dimensions and is adequately sub-square to keep thermal losses low.

You see many piston rings in the design, i.e. you see increased fmep. Count them (the pressure ring at the scavenging pump side seals a pressure of less than 2 bars, i.e. it can be omitted leaving the oil ring to make its work). The piston rings are fewer than the conventional four stroke with the same number of pistons. And the 4stroke has many other power thefts.

The “complication” of the two crankshafts of the single cylinder Junkers-PRE: Suppose you divide equally the load to the two crankshafts (as shown in the http://www.pattakon.com/pre/PRE16.exe animation or in the http://www.pattakon.com/fly/Flyer4.exe animations). The two crankshafts share the same combustion chamber, so the synchronizing gearing carries no loads, just keeps the two crankshafts synchronized (i.e. the power is directly transferred from the crankshafts to the load). The basis of the power plant is absolutely free from inertia AND combustion vibrations.The present trend is the Hybrid cars, where such a power plant seems ideal: absolutely vibration free (from inertia and from combustion), improved thermal efficiency, light weight, small external dimensions, mounted anywhere in the car and so on.

Take also a look at the number of parts and shafts used in the Yamaha TDM two cylinder, 4stroke engine (which has, just like the single cylinder Junkers-PRE, one power pulse per crank rotation). And think that with all this complication the only they achieved is to cancel only the first order inertia vibrations and nothing else.

But I think that, instead of focusing on the details of the mechanism of the PRE engine which is nothing but a modified version of the conventional “crank to connecting rod to piston” mechanism, it is better to focus on the 30 to 40% increased dwell of the piston of the PRE at TDC, which is the core characteristic of PRE.

Do we need such a long dwell?

Does the efficiency of a direct injection Diesel (which now has the best thermal efficiency) increases and how much?

Does the efficient rev range of the direct injection Diesel goes beyond 6000 rpm (i.e. can a naturally aspirating DI Diesel has higher power concentration than a spark ignition engine?).

Originally posted by manolis But I think that, instead of focusing on the details of the mechanism of the PRE engine which is nothing but a modified version of the conventional “crank to connecting rod to piston” mechanism, it is better to focus on the 30 to 40% increased dwell of the piston of the PRE at TDC, which is the core characteristic of PRE.

If the biggest impediment to spinning a diesel faster (and thus getting more HP) is the burn rate of the fuel -- why not use twin injectors? Kind of like the racing Alfas and 911s used to use twin plugs so that they could initiate combustion from both sides of their hemi combustion chamber, and reduce the amount of ignition advance required by their convoluted combustion chamber shape (taking into account the affects of the piston dome). This would decrease by half the amount of time it takes to inject the fuel, increase the area covered by the pattern and would (I think) result in 2x the fuel being burnt in a given amount of time.

If the biggest impediment to spinning a diesel faster (and thus getting more HP) is the burn rate of the fuel -- why not use twin injectors? Kind of like the racing Alfas and 911s used to use twin plugs so that they could initiate combustion from both sides of their hemi combustion chamber, and reduce the amount of ignition advance required by their convoluted combustion chamber shape (taking into account the affects of the piston dome). This would decrease by half the amount of time it takes to inject the fuel, increase the area covered by the pattern and would (I think) result in 2x the fuel being burnt in a given amount of time.

Wouldn't help as a compression ignition engine burn the fuel with a diffusion flame.

Typically the combustion process in a CI engine is improved by higher fuel injection pressures (smaller fuel droplets) and an improved swirl motion of the charge (look how the ports in the head and the piston crown is designed).

Normally the flame is quenched at about half the stroke, so combustion should be complete before that point. Due to emissions the air/fuel ratio must also be kept lean, with a blend richer than about lambda 1.3 soot emissions become a big issue.

On a SI engine turbulence increase proportionally against engine speed, and combustion speed proportionally against turbulence with means that the combustion duration measured in crankshaft degrees is simular during both low and high speeds. In a CI engine combustion speed is rather constant which means a increased combustion duration in forms of crankshaft degrees at high engine speed.

But combustion during very small combustion chamber volume changes are also a problem in itself. Current commericial diesels run combustion pressures of up to 250 bar to fulfill fuel consumption, power and emission demands. Passenger car diesels use somewhat lower pressures, probably up to about 180 bar in the near future. With a smaller change in combustion chamber volume during the heat release peak pressures would be even higher. To handle 250 bar you typically needs a steel piston and an iron head.

Since high combustion pressures demand strong components, these tend to be heavy, this is another problem if you want high engine speeds.

With a CI engine it's usually simpler to make the power though turbocharging since there is no "knock" limit as with SI engines. Unlike an increase in engine speed turbocharging increase the power output without significantly increase the friction losses which is positive for efficiency.

Originally posted by J. Edlund It would probably be difficult to lubricate/cool the pistons with this design. Also, in order to handle the +200 bar peak pressures in a commerical diesel engine, weight of the reciprocating components would most likely also be a problem.

To get a short combustion time, motion of the gas inside the cylinder is important, so some data about this subject would also be needed.

The ideal cycle for the compression ignition engine is a constant pressure or a constant pressure/volume cycle.

J.Edlund

The lubrication of the piston is simple: you need plenty of oil for the thrust loads at the piston pin side, where both cylinder and piston are cool, you also need some oil for the piston rings just like the conventional and the typical Junkers.

The cooling of the piston: the cooling of the conventional piston is difficult because the piston pin and the upper part of the connecting rod “cover” the hot piston head and because the trust loads are transferred to the hot cylinder wall. In the PRE, there is no piston pin (neither con-rod) at the combustion side of the piston, i.e. you can cool the piston head as much as you like (for instance by oil injection, if necessary). The thrust loads are transferred at the other side (the cool side).

A peak pressure of 200 bar on a typical piston of 80mm bore, simply means a force of 10,000 Kp. To get the same inertia force from the piston of the Junkers-PRE (with 50mm piston stroke, i.e. 100mm cylinder stroke, and 75mm con-rod length, at 6,000 rpm) you need a reciprocating mass of 7.5 Kg (i.e. one double piston, one piston pin and the upper part of the connecting rod). Even if the piston of the Junkers-PRE were a solid steel cylinder (80mm bore, 200mm long) its mass is 7.8 Kg.The balance.exe program at www.pattakon.com/educ helps in the calculations.

For the air motion. Open and study the Fuel’s Viewpoint animation at www.pattakon.com/pre/droplet.exe . The conventional at 4,500 rpm and the PRE at 6,000 rpm, at the top 20% of the piston stroke, seem for the fuel identical as regards the volume versus time, while the air turbulence and swirl is much increased in PRE due to the higher revs.

What proportion of the heat loss in a conventional engine goes through the cylinder head? I'm away from my desk, so haven't got any reference books. Does an opposed piston design eliminate this loss, or does it mean that in practice you have to cool the pistons more?

The lubrication of the piston is simple: you need plenty of oil for the thrust loads at the piston pin side, where both cylinder and piston are cool, you also need some oil for the piston rings just like the conventional and the typical Junkers.

The cooling of the piston: the cooling of the conventional piston is difficult because the piston pin and the upper part of the connecting rod “cover” the hot piston head and because the trust loads are transferred to the hot cylinder wall. In the PRE, there is no piston pin (neither con-rod) at the combustion side of the piston, i.e. you can cool the piston head as much as you like (for instance by oil injection, if necessary). The thrust loads are transferred at the other side (the cool side).

A peak pressure of 200 bar on a typical piston of 80mm bore, simply means a force of 10,000 Kp. To get the same inertia force from the piston of the Junkers-PRE (with 50mm piston stroke, i.e. 100mm cylinder stroke, and 75mm con-rod length, at 6,000 rpm) you need a reciprocating mass of 7.5 Kg (i.e. one double piston, one piston pin and the upper part of the connecting rod). Even if the piston of the Junkers-PRE were a solid steel cylinder (80mm bore, 200mm long) its mass is 7.8 Kg.The balance.exe program at www.pattakon.com/educ helps in the calculations.

For the air motion. Open and study the Fuel’s Viewpoint animation at www.pattakon.com/pre/droplet.exe . The conventional at 4,500 rpm and the PRE at 6,000 rpm, at the top 20% of the piston stroke, seem for the fuel identical as regards the volume versus time, while the air turbulence and swirl is much increased in PRE due to the higher revs.

ThanksManolis Pattakos

On a normal engine lubrication of the cylinder/piston is simple. Oil from the crankcase and cooling jets form a film in the cylinder bore and the oil scraper rings remove excess oil. This gives the correct amount for lubrication without an excessive oil consumption. Piston cooling is simple, today most diesels use jets which spray oil into a cooling duct inside the piston which cools the piston very effectivly.

Lubrication of the piston pin is also simple, a hole can be drilled though the con rod which supplies the pin with oil from the crankpin bearing. Other approches are also possible, and in general this works very well.

Lubrication with this opposed piston design will however be a larger issue.

With combustion pressures in excess of 200 bar the demands on all the components in the engine will be high (with less piston motion around TDC pressures would be even higher). With this design it will be very difficult to build main reciprocating components which both will handle these loads and the have a low mass. These kinds of pressures also means high temperatures, so a steel piston must be used. This makes oil cooling even more important since high temperatures will cause the oil film to break down.

As for the in cylinder motion you need to make a CFD simulation for this and compare with a conventional engine. A simple comparison between piston motions isn't good enough.

Regarding the serial hybrid setup, these aren't used these days since thei lack the capability to travel at high speeds for long durations. As an electrical generator there are also several other vibration free solutions that can be used. For example the combined generator/stirling engine (like the crankless NASA design) or a gas turbine with a high speed generator.

Originally posted by Wolf J. Edlund- I don't think that for CI smaller (fuel particle) means better- ISTR that (Steyr) Puch went overboard and managed to disperse fuel in so fine a spray that it wouldn't ignite at all.

Commerical diesels use injection pressures around 2000 bar and that is currently increasing.

Smaller fuel particles means a larger surface to volume ratio, this increase heat transfer to the liquid fuel which should mean a higher evaporation rate and therefore a higher combustion rate. In a CI engine the fuel burn as soon evaporated fuel comes into contact with oxygen, given that the temperature in the cylinder is above the auto ignition temperature of the fuel.

In order to get low emissions it's also important that the fuel mixture is distributed evenly as lean zones cause NOx formation while rich zones form soot (particles).

Originally posted by Greg Locock What proportion of the heat loss in a conventional engine goes through the cylinder head? I'm away from my desk, so haven't got any reference books. Does an opposed piston design eliminate this loss, or does it mean that in practice you have to cool the pistons more?

Isn't the average heat loss something like 25%, of that I would expect that somewhat more heat goes though the head than the piston as the piston is warmer. But I don't thick this will have a large effect on the efficiency of the engine. On the other hand, since the exhaust ports are placed at one piston and the intakes at the other piston one piston and its part of the liner will run hotter which may be a problem. This will be a problem for all opposed-piston designs where the intake and exhaust is placed in such a way.

I don’t know what “serial hybrid setup” is. What I know is that with the following Hybrid Car setup :

the vehicle can travel at high speed as long as there is fuel into the fuel tank:The PRE engine provides, by means of the two electric generators, power to the control box. As long as the vehicle needs all the power of the Junkers-PRE engine, the electrical power from the two electric generators is transmitted to some or all the electric motors. There is no clutch, neither gearbox, nor differential (so the power loss to transform the mechanical power to electric power (at the electric generators) and back to mechanical power (at the electric motors) is, at least partially, offset. When the vehicle needs less power, the excessive electrical power charges the battery. At fast acceleration both, the PRE-engine and the battery (if charged), supply power to the electric motors (for instance the battery to the front electric motors and the Junkers-PRE with the electric generators to the rear electric motors).

The direct injection Diesel Junkers-PRE offers more time (at the right conditions) to the fuel to get prepared and burned efficiently, so it improves the thermal efficiency of the conventional DI Diesel (the present champion of thermal efficiency). The additional dwell at TDC provides also the ability for efficient high revving (i.e. high power concentration). The ability of the Junkers-PRE to rev efficiently at 6000 rpm does not mean that it has to rev at 6000 rpm. But at 4000 or 4500 or 5000 rpm the time for efficient and clean combustion is plenty in comparison to the conventional.

I read in the web (please correct me if I am wrong) that the present crankless electric generators (with heavy magnets secured to the free-pistons to reciprocate with them) have currently a rev limit of only 1800 rpm. With such a slow rhythm you cannot achieve comparable power concentration (i.e. they seem not good for Hybrid cars).

By the way, the Junkers-PRE is no more than the “typical” free piston engine with the addition of two connecting rods, by means of which the linear reciprocation of the pistons is transformed into rotation. And the “remarkable” simplicity of the free piston engine, taking under account the necessary synchronizing mechanism that keeps the opposed pistons in phase, the additional mechanism to milk the power of the gas, the difficult starting etc, is not true in practice.

As for the gas turbines, they are lighter, simpler and more reliable than the reciprocating engines, but their thermal efficiency is, by far, worse than the direct injection Diesel (in the range of 20 to 200 KW per unit). Small helicopters and small airplanes still prefer the internal combustion engine. And the trend in small airplanes is to replace their spark ignition engines with direct injection Diesels to get better mileage and better reliability.

High pressure and components weight.When you are talking for 200 bar combustion pressure, you are actually talking for a kinematic mechanism robust enough to carry the resulting loads. 200 bar pressure on a 80mm bore piston, simply means 10,000 Kp load. I.e. the kinematic mechanism must be strong enough to carry such a maximum load.As I wrote in my previous reply, in case of the Junkers-PRE as long as the mechanism can face such heavy loads, the weight of the piston, piston pin etc does not matter. At 6000 rpm the peak inertia loads implied by the piston – even if it were a solid steel cylinder of 80mm Bore and 200mm height, i.e. 7.8 Kg – have similar strength to the combustion loads from 200 bar pressure. I.e. you can have the strongest possible piston in the world, and still be “light”, since it does not imply heavier inertia loads than the loads from working combustion. Of course a working piston is several times lighter than the solid steel piston, being more than necessary strong to face the high pressure into the combustion chamber.The connecting rod, on the other hand, is shorter and is heavily loaded only in tension, i.e. it is far lighter and far stronger than the conventional connecting rod. In other words, the components of the Junkers-PRE can be more strong than necessary and still light enough.

Cooling: Where do you see the difficulty for cooling the piston of the Junkers-PRE? From the crank-pin you can “see” the whole back side of the piston head. You can – if necessary - inject as much oil directly to the back side of the piston head to cool it. In the conventional, the backside of the piston head is “hidden” from the upper part of the connecting rod and the piston pin, making more difficult the oil spray to reach the hot area.The overcooling is the problem: many direct injection Diesels use a hot steel piston head and constrain its cooling to keep it hot.

Lubrication:In the conventional engine, the worst point to lubricate is the piston skirt. The cylinder wall is hot, the surface pressure high and the oil film “brakes” allowing direct contact of piston and cylinder.In the PRE, the thrust loads are taken at the height of the piston pin, i.e. far away from the hot cylinder wall. What I see is easier and more efficient lubrication. Where do you see the problem?

I copy the reply from another forum (i.e. the following are not my words)“I do like the idea of moving rod angle forces below the crank centerline. It should keep rings in a better position at TDC and reduce piston and cylinder wall wear in that area. My guess is this design of yours may even run quieter that a normal diesel.John”

The point is to take advantage of the considerably longer dwell of the piston at TDC. This is the crux. The combustion efficiency has always been the core issue. The mechanism is just the means (the tool) to achieve the improved combustion. A small increase of thermal efficiency may justify a different mechanism. And the PRE is no more than a modified version of the conventional “crank to connecting rod to piston” mechanism, i.e. a tested, familiar and easy technology.

Even with worse mechanical efficiency, the overall brake efficiency is what counts, i.e. how, from the same quantity of fuel, to milk more mechanical energy.As for the mechanical efficiency of the PRE, I still cannot see where the PRE mechanism is worse than conventional.

The point is to take advantage of the considerably longer dwell of the piston at TDC. This is the crux. The combustion efficiency has always been the core issue. The mechanism is just the means (the tool) to achieve the improved combustion.

No, actually that's where you went wrong. You have sort of an interesting gadget there, but you have selected exactly the wrong application for it, at exactly the wrong time.

Of the various problems identified with the diesel engine, attaining high levels of thermal efficiency is not one of them. They are already pretty darn OK in that regard -- best on the road more or less. To put it another way, thermal efficiency is in no way a barrier or a point of resistance in building and selling as many diesels as we can. It's not a real market problem.

So...what are the real challenges (or opportunities, if you are wired that way) in diesel engine development today? Well, emissions is certainly one of the major ones, in particular oxides of nitrogen. Especially in high-specific output, high-speed diesels, because it is at peak combustion temperatures and pressures that NOx is produced, and most difficult to control. And here we are. We are going to prolong piston dwell through TDC, increasing and extending the peak combustion phase, which is exactly what we don't need.

Don't get me wrong. I have always had a great appreciation for unusual and alternative engine designs. I have been studying them for 30 years, and have collected a rather curious and extensive little library on the subject stretching back another century or so. If there is one thread that winds through the entire narrative it is this: in most cases, the alternative engine is an answer to a question nobody was asking. Folks are forever trying to fix the things that are not really broke.

That is part of the fascination with alternative engines, and it is easy to see how it arose...these ideas tend to come from outsiders, those who are insulated from the industry and not only its conventional thinking but its real, everyday concerns. So these engines are often fresh, original and extremely creative in many ways -- and ultimately futile and forgotten (except to people like me) because they have no practical purpose or commercial application. With alternative engines, funny how often the word "chimera" has come to mind.

I too have an extensive library of alternate engine designs. We should swap files sometime.The only alternate design to make it to production is the wankle rotary despite its poor thermal efficiency and machining problems. It did produce good power and has built a cult following .Cheers malbeare www.sixstroke.com

I don’t know what “serial hybrid setup” is. What I know is that with the following Hybrid Car setup :

the vehicle can travel at high speed as long as there is fuel into the fuel tank:The PRE engine provides, by means of the two electric generators, power to the control box. As long as the vehicle needs all the power of the Junkers-PRE engine, the electrical power from the two electric generators is transmitted to some or all the electric motors. There is no clutch, neither gearbox, nor differential (so the power loss to transform the mechanical power to electric power (at the electric generators) and back to mechanical power (at the electric motors) is, at least partially, offset. When the vehicle needs less power, the excessive electrical power charges the battery. At fast acceleration both, the PRE-engine and the battery (if charged), supply power to the electric motors (for instance the battery to the front electric motors and the Junkers-PRE with the electric generators to the rear electric motors).

A serial hybrid setup is a hybrid car where the engine, generator and electric motors work in a series. This can be compared to a parallell setup where the electric motor and generator work in parallell, or a series-hybrid setup such as used by for example Toyota Prius.

The drawbacks of the series hybrid system is well known, it can't handle high speeds for long duration. This since the engine powering the generator is much smaller compared to a normal engine so it can produced the energy required to sustain high speeds for long durations. What it do allow is to sustain high speeds/accelerations for short durations as long there is energy left in the battery.

Originally posted by manolis The direct injection Diesel Junkers-PRE offers more time (at the right conditions) to the fuel to get prepared and burned efficiently, so it improves the thermal efficiency of the conventional DI Diesel (the present champion of thermal efficiency). The additional dwell at TDC provides also the ability for efficient high revving (i.e. high power concentration). The ability of the Junkers-PRE to rev efficiently at 6000 rpm does not mean that it has to rev at 6000 rpm. But at 4000 or 4500 or 5000 rpm the time for efficient and clean combustion is plenty in comparison to the conventional.

Well, increased time for combustion doesn't mean that the combustion will be more efficient. In a current diesel engine all fuel is burned, so that part isn't a problem. The main problem is that some fuel forms particles while the high temperatures in combination with air excess cause NOx to form.

A diesel is more than 40% efficient at full load, for large engine that can even be above 50%, so that isn't much of a problem. At least not in cars and trucks which run most of the time at par load where frictional losses will be a much larger issue.

Possebly you should consider another application such as ship diesels, these run at high loads and even a possible decrease in fuel consumption at those high loads will be interresting. Also, weight will be a much smaller issue.

Originally posted by manolis I read in the web (please correct me if I am wrong) that the present crankless electric generators (with heavy magnets secured to the free-pistons to reciprocate with them) have currently a rev limit of only 1800 rpm. With such a slow rhythm you cannot achieve comparable power concentration (i.e. they seem not good for Hybrid cars).

I'm not sure what speed they operate at but that isn't that important. The important issue is that they can produce the power needed, do that with a high efficiency and with low emissions without being too large/heavy. The only issue with the crankless stirling engine generator as I see it is the weight/size part.

Originally posted by manolis As for the gas turbines, they are lighter, simpler and more reliable than the reciprocating engines, but their thermal efficiency is, by far, worse than the direct injection Diesel (in the range of 20 to 200 KW per unit). Small helicopters and small airplanes still prefer the internal combustion engine. And the trend in small airplanes is to replace their spark ignition engines with direct injection Diesels to get better mileage and better reliability.

Volvo have had some good results with these in hybrid truck/bus applications. I don't remember the specifics but the turbine used produced something like 100 hp, it was rather simple, a single stage centrifugal compressor and a two stage turbine with a regenerator. The efficiency was slightly above 30%, so it consumed a little more fuel than a diesel hybrid but on the other hand it was much lighter and the exhaust emissions where much lower compared to a diesel. The turbine used ran on ethanol, and only on full load. By allowing higher turbine inlet temperatures and running at higher pressure ratios the efficiency could probably be increased closer to 40%.

Gas turbines as used in helicopters are quite costly so usually these aren't affordable for a small helicopter.

Gas turbines are efficient at full load, the problem is the efficiency at part load but a series hybrid system allows full load to be used at all times. In a small car the engine power requirement is probably around 10 kW which means a turbine not much larger than an automotive turbocharger.

Originally posted by manolis High pressure and components weight.When you are talking for 200 bar combustion pressure, you are actually talking for a kinematic mechanism robust enough to carry the resulting loads. 200 bar pressure on a 80mm bore piston, simply means 10,000 Kp load. I.e. the kinematic mechanism must be strong enough to carry such a maximum load.As I wrote in my previous reply, in case of the Junkers-PRE as long as the mechanism can face such heavy loads, the weight of the piston, piston pin etc does not matter. At 6000 rpm the peak inertia loads implied by the piston – even if it were a solid steel cylinder of 80mm Bore and 200mm height, i.e. 7.8 Kg – have similar strength to the combustion loads from 200 bar pressure. I.e. you can have the strongest possible piston in the world, and still be “light”, since it does not imply heavier inertia loads than the loads from working combustion. Of course a working piston is several times lighter than the solid steel piston, being more than necessary strong to face the high pressure into the combustion chamber.The connecting rod, on the other hand, is shorter and is heavily loaded only in tension, i.e. it is far lighter and far stronger than the conventional connecting rod. In other words, the components of the Junkers-PRE can be more strong than necessary and still light enough.

I don't think you realise how high these loads are, and given a smaller volume change around TDC pressures would be even higher. The loads caused by the +200 bar pressure are extreme. Take a look at the design on any of the diesels running these kinds of pressures and you will see that.

In a normal piston engine the loads caused by the +200 bar combustion will exceed anything the inertia forces can cause. If we talk about diesel with a bore of 80 mm that engine will have a reciprocating weight in the order of 0.5-1.0 kg. Your problem will be to transer this force all through the piston and to the con-rod connection on the other end without the reciprocating weight to become too high.

Originally posted by manolis Cooling: Where do you see the difficulty for cooling the piston of the Junkers-PRE? From the crank-pin you can “see” the whole back side of the piston head. You can – if necessary - inject as much oil directly to the back side of the piston head to cool it. In the conventional, the backside of the piston head is “hidden” from the upper part of the connecting rod and the piston pin, making more difficult the oil spray to reach the hot area.The overcooling is the problem: many direct injection Diesels use a hot steel piston head and constrain its cooling to keep it hot.

Lubrication:In the conventional engine, the worst point to lubricate is the piston skirt. The cylinder wall is hot, the surface pressure high and the oil film “brakes” allowing direct contact of piston and cylinder.In the PRE, the thrust loads are taken at the height of the piston pin, i.e. far away from the hot cylinder wall. What I see is easier and more efficient lubrication. Where do you see the problem?

To cool the piston with oil, or even with water for that matter is not much of an issue with the current diesel engine design. At typical piston temperatures steel is something like 16 times stronger than aluminum and a steel piston can be made at no significant weight disadvantage. This means that piston temperature is in itself no bigger issue, but piston temperature when it comes to lubrication is a issue, which demands cooling.

Since a diesel engine has a "bowl" in the crown the best cooling solution, packaging wise, is to cool the piston around the bowl. You can of course do the same, there will be no bigger difference except some issues with the placement of the oil jets. Also, the opposed piston design will probably have some issues with lubrication of the cylinder. I think it would be somewhat difficult to get the correct amount of oil onto the cylinderwalls.

In a conventional engine design there are no issues with lubrication. Oil is supplied by splash from the crankcase and from the oil cooling jets. The cylinder wall itself is rather cool, only slightly hotter than the coolant with slightly higher temperatures close to the combustion chamber. The oil film lubricating the piston is mainly hydrodynamic with some tendencies to boundary layer and mixed lubrication around TDC and BDC but this is essentially a non issue.

Originally posted by manolis The point is to take advantage of the considerably longer dwell of the piston at TDC. This is the crux. The combustion efficiency has always been the core issue. The mechanism is just the means (the tool) to achieve the improved combustion. A small increase of thermal efficiency may justify a different mechanism. And the PRE is no more than a modified version of the conventional “crank to connecting rod to piston” mechanism, i.e. a tested, familiar and easy technology.

Even with worse mechanical efficiency, the overall brake efficiency is what counts, i.e. how, from the same quantity of fuel, to milk more mechanical energy.As for the mechanical efficiency of the PRE, I still cannot see where the PRE mechanism is worse than conventional.

The thermal efficiency that in theory can be achieved is already high for a diesel engine, any significant change in the mechanical design will not give any significant improvement in thermal efficiency. If you do some calculations on the thermodynamics I think you will come to that same conclusion. The main reason for engine inefficiency is not a combustion problem or a problem with the thermodynamic efficiency of the process used it's more about the heat energy lost as exhaust and you can't do much about that. For lower loads, like the typical automotive use, frictional losses and pumping losses tend to be a bigger issue (which is significantly smaller for the diesel than for the gasoline engine).

With the opposed piston design I also can see no reason for the "outer" extra set of pistons. Are these supposed to be scavenge pumps? Pistons pumps are not used as scavenge pumps for a very good reason. Screws or a set of turbochargers will to the job a lot better. Plus, it would make lubrication of the cylinder a bit simpler.

A few years ago Ford and GM made big money from SUVs and pick-ups. Today they lose big money from SUVs and pick-ups. If someone could predict the market’s needs, these companies would pleasantly give half of their profits to the prophet.

When Wankel proposed his rotary engine, market had no such a need. Wankel set the problem and also proposed the solution. Billions of dollars were spend from many car makers to finally discover in practice that there were more problems than solutions in Wankel’s engine.

Toyota Prius is not just a hot seller, it became the flag of Toyota, the reference point, the car that raises Toyota’s prestige. The customers know that the additional money to buy a Prius will never return from the better mileage. But they know they drive the state of the art car. And they feel good to pollute less and be among the pioneers.

The market is not standstill. It is alive. It changes every day.A little higher oil price and everybody starts talking about alternative fuels and fuel efficiency (remember a couple of months ago?). A little lower oil price and the alternative fuel projects are all forgotten.

And many times the “need” or the problem is not obvious. Muhammand Yunus (this year Nobel price laurel for peace) from Bangladesh describes how difficult was, at start, to convince people to borrow money from him. I.e. the “market” in Bangladesh did not know it had such a need. Yunus created it. He set the problem and also gave the solution.

A way to predict (not necessarily correctly) the future, is to study the current patents. For instance the Variable Valve Actuation (or VVA) may seem complicated today (the conventional valve train system dominates for so many decades). But the PROBLEM exists. In the US Patent office there are already granted some 1,100 patents (most in the last decade) for VVA valve train systems, i.e. valve train systems providing variable valve lift and/or variable valve duration. Most of them belong to car makers (like Honda, Nissan, Toyota, BMW etc), others to independent inventors.

The Pulling Piston Engine (PPE) is the father of the Pulling Rod Engine (PRE). Take a look at www.pattakon.com/ppeAlso take a look at Pattakon’s US patent 6,062,187 (for PPE) and then at the four year later HONDA’s endeavour on the same exactly PROBLEM with the US patents 6,763,796 and 6,786,189 (at http://www.uspto.gov/patft/index.html ). The following drawings, from Honda’s patents, give a brief idea.

It uses two long connecting rods per piston and a long piston pin that exceeds outside the cylinder.

Think what the target (or need, or problem) is. Think if such a problem is an existing one or a chimera. Spot on the complication of each solution.HONDA’s patents start with “To increase thermal efficiency by increasing the degree of constant volume of a fuel-air mixture at the time of combustion in an internal combustion engine.“ Would you ever say that Honda deals with chimeras?

So there is a real problem. It was and it will be the core problem of all engines: to increase even more the thermal efficiency and to increase even more the power concentration (provided the rest characteristics of the engine stay acceptably good).

EMISSIONS and PREYou wrote that the longer dwell at TDC of PRE will increase the NOx.Let me explain, theoretically, why the PRE is better, or at least equivalent, to the Conventional in this area.

Open the Fuel’s ViewPoint animation at http://www.pattakon....re/droplet.exe and the http://www.pattakon....man/pre_TDC.GIF plot. The combustion process into the PRE revving at 6000 rpm and the combustion process into the Conventional (with the same stroke and the same con-rod to stroke ratio) revving at only 4500 rpm are identical (further, the PRE prevails in that the air turbulence and swirl is increased due to the higher revs). The formation of NOx into the conventional at 4500 rpm and into the PRE at 6000 rpm is similar (note here that after the combustion into the PRE the gas expansion is considerably faster than into the slow revving Conventional, allowing less time to the Nitrogen to find and connect to Oxygen to form NOx, as chemists say). The ways to prevent the formation of NOx in Conventional revving at 4500 rpm (for instance multiple injection, special form of combustion chamber, fuel injection pressure, fuel quality etc) are all applicable to the PRE revving at 6000 rpm. Also the ways, applicable in Conventional, for after treating the exhaust gas are applicable, too, for the PRE.

To summarize: the fuel entering into the combustion chamber cannot “see” the kinematic mechanism. What it sees and touches are the cylinder walls and the compressed/hot air. All the important events of combustion, especially in Diesel, take place into less than the top 20% of the piston stroke. At this area, the volume into the Conventional revving at 4500 rpm and the volume into the PRE revving at 6000 rpm are identical, microsecond by microsecond (try to define, in the Fuel’s ViewPoint animation, which is the Conventional at 4500 rpm and which is the PRE at 6000 rpm), i.e. the volume versus time plot is the same for the two engines. So the pressure, and the pressure rise (dp/dt), and the second derivative of the pressure, and the temperature have to be identical, as well as the NOx (and the rest pollutants, like smoke) formation. The increased turbulence/swirl and the faster expansion is another advantage of PRE.

What happens in lower revs? For instance when the PRE is revving at only 3000 rpm (i.e. 6000/2)?Again the PRE revving at 3000 rpm is identical – as regards the volume versus time at the top 20% of the piston stroke – to the Conventional Diesel revving at 2250 rpm (i.e. 4500/2). You can inject the fuel at exactly the same piston position using the same injection pattern, and expect the same torque and the same pollutants. Similarly for the rest revs.

Look at the additional time provided by the PRE at TDC as freedom to the researcher / developer to select the right injection advance and the right injection pattern without the restrictions of lack of time of conventional in order to get the best (as regards power, efficiency, noise etc) from the Diesel engine. I.e. provides more options to the injection timing and to the injection duration whatever it means.Russel Bourke claimed that his engine had cooler exhaust gases, and this is the result of the longer duel at TDC, this is the recipe of a better efficiency as Sir Ricardo said a Century back…

When “everyone knows” something to be true, nobody knows nothing: Andy Grove, chairman of Intel and co-inventor of the integrated chip, probably the most powerful invention of the 20th century. You and me can communicate now only thanks to this invention and to another great man, Tim Berners-Lee, the inventor of Internet.

As regards the Hybrid cars, with 60 KW you can reach 170 Km/h top speed. If the prime mover of the Hybrid car, either in serial or in parallel arrangement, provides this power continuously, the car can keep this speed as long as there is fuel in the tank (and a few Km/h more as long as the battery is still charged).

Saying that 40% thermal efficiency is enough, is not reasonable. 41% is better than 40%, and 42% is better than 41%. This way the world proceed. If, in order to increase slightly the efficiency, you need disproportionally higher cost and complication, forget it. Otherwise go for it.

I am confused to hear that the power concentration of the “crankless” power plants is not important and only the efficiency matters. It is not so.

For the emissions read what I replied to McGuire.

I wrote twice for the 200 bar and the ability of the PRE to carry such loads. If anybody else can explain better than me, please do. 200 bar on a 80mm bore piston, simply means that the force on the piston is 10,000 Kp. The conventional uses a connecting rod (i.e. a “long” rod) to transfer this compressing load to the crankshaft. The piston of the Junkers-PRE can transfer this load from the combustion side to the scavenging side by means of four feet, each one capable to carry heavier load than the conventional connecting rod. The loading of these four feet is in compression only, i.e. simpler than the loading of the present connecting rod. I also explained that even in the case the piston of the Junkers-PRE is made from steel, it implies inertia loads several times lower than the combustion loads on the kinematic mechanism. What is so difficult to understand? 200 bar is nothing but 200 bar. There is nothing magical with 200 bar. Just loads that have to be transferred through the metal. Tell me the load to transfer from the upper to the lower part of the Junkers-PRE double piston and I will design the piston (from aluminium or steel). And why to keep the weight at 0.5 or 1 Kg? Who puts this limit? If I have the half stroke (Junkers-PRE), i.e. the half piston speed and piston acceleration, and if I have a much lighter connecting rod than conventional (because it is loaded in tension) why to keep the piston as light as the conventional?

The temperature of the conventional cylinder wall is higher close to the combustion chamber and also at the two sides where the piston skirt transfers the thrust loads. The form of the conventional piston is elliptical. There are no such issues in PRE.

The combustion is the stake, the meat. The rest are details.A little improve on combustion has a significant effect on all consequent processes. For instance the combustion of all the fuel at better conditions of pressure/temperature (and the faster expansion that follows) result in significantly lower exhaust gas temperature. Read in the web for the Bourke engine. Here is the Pattakon harmonic engine (pure sinusoidal piston motion, absolutely balanced even as single cylinder) made more than ten years ago.

Its long piston dwell near TDC makes the difference. The PRE engine offers twice the increase of piston dwell at TDC of harmonic and Bourke.

As for the scavenging pistons, they are very important. No turbocharger, no blower, no roots can provide the broadband characteristic of these, almost zero dead volume, built-in scavenging pumps. This is the way to have a two stroke with more flat torque curve than the best four stroke. Think about is.

Me. With complete confidence I can assure you that the world does not need and is not going to buy a diesel engine that is less fuel-efficient than current designs, costs more to produce, weighs more, and produces greater emissions.

Me. With complete confidence I can assure you that the world does not need and is not going to buy a diesel engine that is less fuel-efficient than current designs, costs more to produce, weighs more, and produces greater emissions.

McGuire,

You are not the market. So you cannot decide what market needs.

You are neither confidence enough in what you write, otherwise your arquements would be pure technical, not like "in general".

I used Honda's patents only to show you the core problem the increased dwell at TDC comes to solve. Did you read them? Is the longer dwell the core problem?

Can you, please, explain technically why the PRE has less fuel-efficiency than current designs? Can you, please, explain technically what makes Junkers-PRE to cost more to produce and to weight more?

The Junker-PRE prototype is not yet finished, but most parts of it have been built. Beleive it or not they are simple to make with simple tools. And the engine will weight not "just less" than conventional of same power output but "by far" less.

I also explained the potential of the PRE as regards emmisions (NOx, smoke etc). Please DO follow my simpleminded and pure technical explanation and tell me where the mistake(s) are.

Manolis,
In the couple of years I've been on this site, I've not once seen anyone bring a new twist to the table without almost everyone beating it down, rightly so or not (I'm not nearly as smart as I pretend to be). Folks that 'know' you're wrong don't want to be bothered with explaining why, you should simply accept that they are right, and you are wrong. The one exception to this I've seen is Malbear and his 6-stroke (though I often wonder how he was inititally greeted).

No question a good portion of this is going over my head, and I have no idea if you're crackers or brilliant but I've enjoyed it none-the-less. Thanks for bringing it here.

Originally posted by McGuire Me. With complete confidence I can assure you that the world does not need and is not going to buy a diesel engine that is less fuel-efficient than current designs, costs more to produce, weighs more, and produces greater emissions.

Sounds like you're describing every up-size engine option that has ever been made available, gas or diesel. Care to clarify?

I entered the Invention section as a young man with brown hair ( now grey and not much)I explained how it worked to the judges and then started it to exclamations of " good god it actually runs" They must have thought it was an april fools joke.I proceeded to do the usual slow motion burnout trick at idle. As I did so a Nameless Jealous machinery dealer suddenly jumped on the back of the bike in an attempt to stall it, it didn't , so I proceeded to open the throttle a bit and dug a six inch hole down to the brake drum. cheers all round , but the judges could not bring themselves to give a prize. So the patron of the section Gave me his own personal encouragement award.

Do you believe the market is searching for an engine that is less efficient, more costly and heavy, and has an emissions problem?

To ask this question another way, have you ever considered why the marketplace has already rejected the opposed-piston two-stroke engine for road use?

Originally posted by manolis

You are neither confidence enough in what you write, otherwise your arquements would be pure technical, not like "in general".

I am limited by the information you have presented. You have a few amimations and a number of ambitious claims, but no data and no specifications. And you have no running prototype.

So you have some ideas... but unfortunately they happen to be mistaken. Your approach is obviously based in large part upon the Bourke engine, which is featured on your web site and mentioned frequently in your descriptions. You are either unconcerned or unaware that the Bourke engine is a crackpot invention, a product of delusion and/or fraud. Despite numerous and exhaustive attempts, the dubious claims of the late Russell Bourke have never been duplicated.

Originally posted by imaginesix Sounds like you're describing every up-size engine option that has ever been made available, gas or diesel. Care to clarify?

Sorry, I don't follow your analogy. When you check the order box for the optional engine, presumably you get a little more output (or if there is a diesel available, better economy). If you were to choose this engine, you get less of everything for your extra money. How is that a deal? There is no reason for you to check that box, or for the manufacturer to offer it for that matter.

There were and there are some successful applications of the Junkers engine, as on military applications (Russian tanks) and on small civil airplanes (DAIR : 100 PS from 92 Kg direct injection Naturally Aspirating Diesel). The TS3 opposed piston engine with a single crankshaftwas a sophisticated design. Despite its over-complication and its additional friction, it was a successful design in its days.I copy from a letter to the green car forum:“the best opposed piston two-stoke diesel engine built and fitted in a vehicle was, as been mentioned, the Rootes TS3 engine fitted in Commer trucks from 1954 to 1972, using one crank and large rockers. It had an amazing power to weight ratio for the time, impressive even today, and was remarkably economical with other similar powered trucks consuming twice the fuel. A much improved 4 cylinder version, the TS4, was developed and was just about ready for production when the dreaded Americans came along. Rootes had fallen into financial problems because of poor management in the car division. Chrysler swept in, in 1968, and bought out Rootes. They didn’t understand and eventually dropped the remarkable TS3 motor and ordered the 14 prototypes of the TS4 scrapped. The last TS3 engined truck was in 1972. Only a few TS4 prototypes were scrapped, with Rootes staff hiding them or using them as backup generators to preserve them. Chrysler wanted their existing engine ranges, or contracts with Cummins, to used and replaced the TS3 with an antiquated Cummins unit – the specs sheets alone should have told the Chrysler engineers that the TS4 engine was something special. With such crass stupidity and lack of foresight no wonder Chrysler went belly up. They were only interested in vested interest, not advancement.A few TS4 engines have made their way to New Zealand where they were brought back to new condition, with one about to be fitted in a revamped Commer truck. A few people are looking into installing modern fuel management systems of the TS3. The TS3 is still used in boats and the likes mainly in Australia and New Zealand. This new web site is dedicated to the TS3 and TS4 engines, with lots of info on all types of diesel two-stokes. Nice one Kiwis! http://www.commer.org.nz ”

On 2003 the first Pattakon VVA prototype car was on the roads for drive tests. Every now and then it was pressed to its limits. The fear was to break the underneath mechanism (crankshaft, pistons, connecting rods).After the refusal of car makers and of universities to respond, the Pattakon VVA was published to many forums to be known to the public and get opinions and objections.In TOV forum (the most relevant forum to the object), after many refusal and stupid “objections” like “what color your shocks (or skin) are”, they persistently did not believe the mechanism could work, neither that a prototype were really made and working on real conditions. I proposed to the administrator of the forum to come in Athens, drive the car and write his impressions. He was absolutely negative saying there was no prototype. I proposed/bet to pay his airplane tickets to come in Athens to see and drive the car. Here is a paragraph of his written reply :

“So, Manolis, rather than doing anything to convince me further that you are right...this has, conversely, convinced me even more that you do NOT have a running engine. It has heightened my suspicions that you ARE, in fact, a mendacious charlatan (ooh, three point words!).”

I was driving the car every day and I had to prove “I was not an elephant”.The car (Renualt 19, 1400cc) is still working with the initial “hand made” Pattakon VVA mechanism on it.The next Pattakon VVA prototypes (Honda Civic) are also for years on the roads revving from 330 to 9000 rpm (no other continuous VVA on the world can).It is not yet adapted by the car makers, but this fact does not mean it is not successful. It has proved better than what theory predicted.

Here is the light version (Pattakon roller VVA only on the intake valves)

Take a look at the video at www.pattakon.com/vvar/OnBoard/A1.MOV (QuickTime format, 4MB) of the Pattakon VVA Honda Civic prototype running on public road at 9,000 rpm. The same engine idles at 330 rpm (read the www.pattakon.com/vva/VVA_Idle/VVA_Idle.htm ). For more about Pattakon VVA (Variable Valve Actuation) see at www.pattakon.com , all the underlined topics at the left side. BMW’s valvetronic (lost motion VVA) cannot rev high (above 6,500 rpm), so they cannot use it on their sport cars neither on their bikes.Four years ago it seemed “chimera” to design, built, install and adjust such a system on existing cylinder heads. Now it is more reliable than the rest car.

The story is similar in case of PRE. Invent, design, calculate, patent, built prototype and take opinions/objections from anywhere.

McGuire, everybody knows the safe side “a new design has much more possibilities to fail than to succeed”. The real challenge is to predict “why” the new design will fail.

You persistently (and correctly) write that “the world does not need and is not going to buy a diesel engine that is less fuel-efficient than current designs, costs more to produce, weighs more, and produces greater emissions”. But, the same persistently, you refuse to explain why the PRE engine is less fuel efficient or more costly or more heavy or more pollutant than conventional. This is the point.

To say that you are pretty confident, does not count on technical discussions.Charles Duell, head of US patent Office, was confident (on 1899) to say “everything that can be invented has been invented”,Ken Olson – Digital Equipment president - on 1977 was confident saying that “there is no reason for any individual to have a computer in their home,And Bill Gates was confident saying (on 1981) that 640 KB memory ought to be enough for everybody,

McGuire, help me save time and money by proving to me that the PRE engine has at least one of the bad characteristics you write. Just one. Because one is enough to withdraw the PRE project. Can you, please?

Your engine is going to be overweight because it has two crankshafts rather than one, and will also require a train of very heavy gears to connect them, increasing weight further.

The block will also be overweight due to the opposed-piston layout, and also due to the use of piston-pump tandem scavenging instead of a far lighter and smaller Roots blower or similar. The package is not only heavy; it is very bulky too. It is rather difficult to imagine how it could be made to fit in a conventional passenger car. A car would have to be designed around it somehow.

Two-stroke diesels have been viritually eliminated from the highway over the last few decades, due to their low efficiency and high emissions. At one time nearly city bus in America was a two-stroke, and most trucks as well. Today they are nearly all gone, replaced by cleaner and more fuel-efficient four-strokes.

Again, don't get me wrong. I think the Commer knocker was quite a little engine in its day and a fine example of rowing against the tide. And I believe there are one or two Commer enthusiasts in this forum as well. But looking back in fondness is one thing, and trying to return to the past is another.

Now, sometimes there are market changes or advances in processes and materials technology that allow us to revist old ideas such as these and make them productive again. I don't see that here. Opposed piston two-strokes are still dirty and thirsty, while economy and emissions are still major market forces. The Commer is at least as obsolete today as it was 30 years ago. Nothing has changed in that regard.

We need to ask: how does an opposed-piston configuration move the ball forward today? What problem does it solve? How is it any better? If it's not a clear and significant advance, simply a lateral move for the sake of being different, that is not good enough.

In the prototype under construction the architecture and the dimensions are similar to:

the basic change is the length of the con-rods which are now 75mm from center to center for a 50mm (per) piston stroke, and the bore of the pistons that became 81mm (to use available piston rings).The maximum dimension of the engine is less than 570mm. Its form is like a “long” tube. The capacity of this single cylinder engine is 515 cc (81mm bore, 100mm stroke). To get a 1000 cc engine you combine two such cylinders. They share the same two crankshafts (each crankshaft has two crankpins at 180 deg angular distance for even firing). The maximum external dimension of this 1000cc engine is again less than 570mm.The peak power from a 1000cc two stroke engine is expected to be similar to the peak power of a four stroke with capacity between 1600 and 2000cc (the built-in scavenging pumps provide better potential) .

Having the “block” of the two cylinder 1000cc Junkers-PRE you can easily “hide” it into the cylinder head of the Honda Civic 1600cc. By the way, the cylinder head of the Honda Civic weighs some 23 Kg.

Please take another look at the dimensions of the Junkers-PRE. All bikes have a free space between rear and the front tyres of more than 650 to 700mm. The Junkers-PRE (500cc single cylinder or 1000cc 2cylinder, i.e. more power/torque than any bike can handle) can fit longitudinally:

Do you have to built a car around this “bulky” and heavy engine?

Compared to the conventional engines, the 100mm cylinder stroke for 81mm bore is a very sub square design for compact combustion chamber and low heat loss.

As for the weight.The assembly of each piston with its piston pin and with its connecting rod is less than 1,4 Kg. The counterweights on the crankshafts can be light enough because they balance only the crank pin mass and the lower part of the light connecting rod. Each crankshaft is less than 2.35 Kg (by far oversized). Total mass of moving parts (excluding the synchronizing gears) : 7.5 Kg.

By the way, the piston crown (and the pressure ring land) is from iron. Does anybody knows to tell me whether the iron crown is better of worse?

Weight and bulk of the synchronizing gears:

The short – compared to the conventional Junkers engines – piston stroke and the specific arrangement of the moving parts keeps the distance of the two crankshafts far shorter. For 100 mm cylinder stroke the crankshaft to crankshaft distance (center to center) is below 280mm. To bridge two shafts being in such a short distance is easier, more accurate and lighter. For applications like power plants with twin electric generators (for instance for Hybrid Cars) or twin propellers (for instance for flying machines like the ones shown at www.pattakon.com/fly/Flyer4.exe ), i.e. applications where the load is equally distributed to the two crankshafts, the synchronizing gearing is anything but bulky and heavy because it does not carry loads. Its only work is to keep the two crankshafts (which share the same combustion chamber and the same instant pressure) synchronized.

For applications like autos, trucks and bikes, the following arrangement seems reasonable:

Compare this “primary transmission” to what more than 90% of the present bikes use (like the Yamaha TDM photo in the first page of this thread). A gear secured to the crankshaft is meshed directly to the clutch gear. Compared to the conventional primary transmission of bikes, this one has improved efficiency because the central clutch gear undergoes two equal and opposite forces (again: the two crankshafts share the same instant cylinder pressure) thereby its bearing undergoes no load. As for the size of the gears, taking under account the short distance of the two crankshaft, with a nominal diameter of 110mm for the gears on the crankshafts, the nominal diameter of the clutch gear result in 165mm. Nothing special or bulky or heavy.

For cars and trucks the primary transmission needed for Junkers-PRE does add complication compared to the single crankshaft conventional engine design. The elimination of the cylinder head and the half piston speed justify, by far, the presence of the primary transmission in the Junkers-PRE design.

The prototype (single cylinder, 81mm bore, 100mm cylinder stroke, 515cc) is expected to have a weight of less than 35 Kp making a peak power of more than 70 PS at 6,000 rpm (direct injection Diesel). Direct injection spark ignition seems more suitable for bikes.

Take a look at the typical opposed piston engines. The piston skirt has double role: it opens and closes the intake (or exhaust) ports, it also transfers the thrust loads to the cylinder. To avoid oil consumption and emissions you need as less oil as possible on the piston skirt, but to keep the piston from not coming in contact to the cylinder wall you need plenty of oil otherwise the hydrodynamic lubrication fails. You cannot have both of them. The compromise is unavoidable: small bore, long stroke, long connecting rods and oil in the exhaust fumes. The longer the connecting rods and the piston stroke, the longer the crankshaft to crankshaft distance and the longer the maximum dimension of the engine. With long distance between the crankshafts you need more gears to synchronize them (from one end of the engine to the other).Follow the same in case of Junkers-PRE: the skirt of the piston at the combustion side does not transfer thrust loads. You need oil just to keep the compression rings wet, because the thrust loads are taken at the other/cool side of the double piston (far better conditions than the conventional 4stroke, compared to which the Junkers-PRE has also no leakage from the intake valve guides). And so on.

Emissions:Without oil on the exhaust, the Junkers-PRE has no reason to pollute more than the conventional 4stroke Diesel. I explained it following the volume versus time diagram. Read it again. It is a simpleminded explanation but also direct. It is also easy to check it step by step and prove me wrong. Just saying that with a few thermodynamic calculations somebody predict the reality, is neither reasonable nor applicable. In any case, if anybody can do such calculations to prove the Fuel’s Viewpoint explanation wrong, please do.

Built-in scavenging pumps versus roots etc. The built in scavenging pumps does not compare to any other scavenging pump like roots or blowers or turbo and any fan. Every one of these solutions has its own problem. The zero dead volume of the built-in pumps guaranties constant volumetric efficiency over a broader rev range, without additional cost, transmissions and unreliability, especially in transient conditions.

I entered the Invention section as a young man with brown hair ( now grey and not much)I explained how it worked to the judges and then started it to exclamations of " good god it actually runs" They must have thought it was an april fools joke.I proceeded to do the usual slow motion burnout trick at idle. As I did so a Nameless Jealous machinery dealer suddenly jumped on the back of the bike in an attempt to stall it, it didn't , so I proceeded to open the throttle a bit and dug a six inch hole down to the brake drum. cheers all round , but the judges could not bring themselves to give a prize. So the patron of the section Gave me his own personal encouragement award.

Having seen this engine in person and seen it run exactly as advertised, I am more than happy to say I was very impressed with it.This is one of the 'odd ones' that isn't a conventional engine that really really does work, and work well.

It’s a fact that opposed piston engines have the best power density of all the diesel configurations. The Ukrainian tank engines KhKBD develop 1000 hp or even 1150 hp with a displacement of 16 liters (6 cylinders, 12 pistons, 120 x (2 x 120) mm). The problem with such a concept is, as you state oil consumption. Since the piston skirt must be somehow lubricated, some oil must be allowed past the scraper rings and it goes out by the ports. Not much of a concern for a military engine, but for automotive propulsion…http://milparade.udm...ity/31/042x.htm

Your design is very clever. I hope this problem could be lessen as you explain, but don’t you have to still lubricate the piston skirts and let some oil escape?

Another point is about piston acceleration. The Junkers Jumo 207 could safely rev at 3000 rpm with 2 x 160 mm stroke, which is a mean piston speed of 16 m/s. The 24 cylinders Jumo 223 even attained 17,6 m/s at take off power. This was with steel piston crowns and heavy, long pistons! The thing is in a 2-stroke engine, the inertia force acting on the piston around TDC is counteracted at every stroke by the compression and combustion pressure and I guess that’s what allowed those engines to rev so fast.

But, if you invert the dissimilarity in piston acceleration as you plan to do, the strongest acceleration will happen at BDC instead of at TDC. That is just the opposite of what is needed for a 2-stroke engine to be able to withstand fast revving. And your engine is precisely intended to rev fast: 6000 rpm with 100 mm stroke means a mps of 20 m/s, which is quite out of the window for a diesel. OK, there ‘ll be more time for combustion, but the problem becomes piston acceleration at BDC then, especially with such long and heavy pistons (yes, steel would be better for the piston crowns) and short conrods.

Another point: to provide a broad torque and power band, the injection should be retarded at idle and low revs, isn’t it ?

Another point : the bore of the scavenge sides of the cylinder should be much bigger since the volume of scavenging air should be at least 1.5 x the working cylinder displacement. Have a look at a gas generator such as the Sigma GS 34.

Oil is consumed in every engine. Always a small quantity will find the way to the combustion chamber and to the exhaust. The point is to minimize this oil “leakage”. The most common question in TOV forum (strictly technical) is the increased oil consumption of the Honda VTEC cars: keeping the engine above the VTEC point (i.e. above 5,000+ rpm) the engine consumes oil and the only you can do is to check the oil level regularly).More than a decade ago Orbital proposed a direct (air assisted) injection 2stroke spark ignition engine. They used the “dry” crankcase as a scavenging pump. They provided a controlled tiny quantity of oil to the bearings and to the piston skirts. The impressive was that their oil consumption was, by far, less than most decent 4stroke engines. And their piston skirt (transferring the typical thrust loads) had to be kept from not coming in contact to the cylinder wall. What I want to say is that the necessary quantity of oil to keep “oiled” the piston skirt and the compression rings is tiny. The real problem is to have a good oil ring to allow only this minimal necessary quantity to pass to the piston skirt and to the compression rings side. In the Junkers-PRE the absence of thrust loads (at the combustion side of the piston) makes things easier in comparison. And as long as the quantity of oil that finally “escapes” is comparable to the oil consumed in 4stroke “decent” engines, the oil consumption problem is solved.

In the Junkers-PRE the inertia force at TDC is also counteracted (the percentage depends on the revs) at every stroke by the air pressure into the combustion chamber. The strength of the inertia force on the piston is almost double in BDC than in TDC. The Junkers-PRE at 6,000 rpm, with 100mm “cylinder stroke”, i.e. 50mm piston stroke, has 10m/sec mean piston speed (and not 20m/sec as you write), 1350 g acceleration (g=9.81m/sec2) at BDC and 700 g acceleration at TDC.The connecting rod of the Junkers-PRE is heavily loaded only in tensionI.e. on one hand there are relatively weak inertia loads (compared to the combustion loads and compared to the inertia loads of same “cylinder stroke” conventional) while on the other hand there is ideal loading of the connecting rod, i.e. heavy loads in tension only.

To get the importance of the tension loads: the Junkers-PRE in every cycle tries to straighten the connecting rod while the conventional with the combustion loads tries, in every cycle, to bent its con-rod (column loading) :

Think also that at half the maximum revs, the inertia force is 4 times weaker while the combustion force is the same strong. In 1/3 of the max revs the inertia force is 9 times lower and so on. In other words the mechanism of any engine has to be strong enough to carry the combustion forces with and without the “assistance” of the inertia forces.

According the lab data in Tayllor’s book “Internal Combustion Engine”, the friction coefficient increases rapidly with the piston speed. The slow pistons of the Junkers-PRE (10m/sec at 6000 rpm for the prototype Junkers-PRE with100mm “cylinder stroke”) seem a good advantage for friction reduction.

The injection at low revs and idling will be retarded. Think the case you inject, at low revs, the fuel so retarded that the combustion starts on or a little after TDC and compare it to the case a good part of the fuel is already burned before the piston reaches TDC (which is the case in conventional due to lack of time). In the last case you increase the pressure/temperature of the mixture into the cylinder by burning a part of the fuel before TDC and then you continue compressing the mixture: anything but good for efficiency, exhaust gas temperature, noise and pressure/temperature/emissions.

I think you mean an arrangement like this.

It is very similar to the typical “free piston engine” with the addition of a pair of connecting rods. For the moment the 1:1 scavenging volume to working volume ratio is being chosen as simpler.